The study, published Monday in the medical journal JAMA Pediatrics, analyzed data from more than 64,000 children in Denmark between 1996 and 2002. (Credit: Getty Images)

But a new study out of Denmark suggests the use of acetaminophen during pregnancy could be associated with ADHD-like behavioral problems in children.

“(Pregnant women) shouldn’t worry at this point,” says study author Dr. Beate Ritz, professor and chair of the epidemiology department at the University of California, Los Angeles. “But if I were a woman who was pregnant … I would try to avoid taking painkillers as much as I can until we know more about this.”

The study, published Monday in the medical journal JAMA Pediatrics, analyzed data from more than 64,000 children enrolled in the Danish National Birth Cohort study between 1996 and 2002. Mothers in the cohort study reported on their children’s behavior, and the researchers looked at databases to determine how many prescriptions for ADHD drugs were written and how many children received a diagnosis of a severe form of ADHD called hyperkinetic disorder, or HKD.

The study authors concluded that prenatal exposure to acetaminophen may increase the risk of a child being diagnosed with HKD or being prescribed ADHD medications and “exhibiting ADHD-like behaviors.” It’s important to note that ADHD-like behaviors are not the same as having ADHD.

An accompanying editorial published in JAMA Pediatrics emphasizes that the study has found “an interesting observed association,” but that the researchers did not find that acetaminophen causes ADHD. The study authors agree that their results do not show a cause-and-effect relationship.

The data suggests that taking acetaminophen for longer periods and later in pregnancy is associated with higher risks, Ritz says. When women reported use for 20 weeks or more, their children had a 50% increased risk for receiving ADHD medication, according to the study.

Ritz says more than half of all mothers in the study reported some acetaminophen use while pregnant. The study measured how many weeks the mother reported taking any amount of acetaminophen but did not take the dosage into account.

“When used as directed, Tylenol has one of the most favorable safety profiles among over-the-counter pain relievers,” said McNeil Consumer Healthcare, the maker of Tylenol. “We are aware of the recent JAMA Pediatrics study; however, there are no prospective, randomized controlled studies demonstrating a causal link between acetaminophen use during pregnancy and adverse effects on child development.”

The study’s authors suggest that acetaminophen may increase the risk of ADHD by interfering with maternal hormones that are critical for fetal brain development, citing a previous study done using acetaminophen in rats and a study of acetaminophen and autism done with humans.

“The cited literature is not relevant to the human condition,” says Dr. Max Wiznitzer, pediatric neurologist and associate professor at Case Western Reserve University School of Medicine. “I’m afraid that (women) will think, somehow, that they caused their child’s problem when the study does not tell us that. It tells us that they are linked but does not tell us how.”

“There are a lot of variables that still need to be considered, such as the fact that ADHD runs in families,” Wiznitzer says. Seventy to 80% of ADHD cases are hereditary, he says.

The study highlights the importance of not taking a drug’s safety during pregnancy for granted, the accompanying editorial points out.

“There are nonpharmacological ways to deal with pain,” says Dr. Jeffrey Chapa, head of maternal-fetal medicine at Cleveland Clinic Children’s Hospital. Massages, baths and acupuncture are some alternatives he suggests to help relieve pain. “I think we have to focus a little bit more on that as opposed to just medications.”